With the rapid development of industrial technologies, multimedia products have been improved on a regular basis to provide more satisfaction to their users both visually and aurally. In order to make the most of acoustic resonance and generate the desired acoustic field, it is common practice to dispose a low-frequency loudspeaker and/or a high-frequency loudspeaker in an enclosure, whose internal cavity functions as a resonant cavity.
Please refer to FIG. 1 for a conventional loudspeaker enclosure structure 10 which essentially includes a hollow housing 11 and a cover 12. The front side of the hollow housing 11 is provided with an opening 110. Two opposite side walls 111 of the hollow housing 11 extend linearly backward in a converging manner from the periphery of the opening 110 to a rear wall 112 of the hollow housing 11. The other two opposite side walls 113 of the hollow housing 11 extend backward parallel to each other from the periphery of the opening 110 to the rear wall 112. An installation bracket 16 is pivotally connected to the side walls 113 so that the hollow housing 11 can be fixed at a proper location. An audio control circuit 13 is mounted in the hollow housing 11, or more specifically on the inner side of the rear wall 112, and is configured for receiving audio signals from an audio power amplifier (not shown) and performing audio processing on the signals. The cover 12 is sized to be fixed to the periphery of the opening 110 and is provided with a low-frequency loudspeaker 120, a high-frequency loudspeaker 121, and at least one bass reflex port 122. The high- and low-frequency audio signals generated by the audio control circuit 13 are respectively transmitted to the high-frequency loudspeaker 121 and the low-frequency loudspeaker 120, causing the membranes thereof to vibrate and make high- and low-frequency sounds respectively. Typically, a sound absorbing material 14 made of nonwoven fabrics or foam is placed between the cover 12 and the audio control circuit 13 of the loudspeaker enclosure structure 10 to absorb low-frequency vibrations, thereby preventing the signal wires and power wires on the audio control circuit 13 from low-frequency resonance, which, if present, will interfere with low-frequency output from the loudspeaker enclosure structure 10. In addition, a dust shield 15 having a web-like structure is provided on the outer side of the cover 12 to protect the loudspeakers 120, 121 and keep dust and other foreign matter from entering the loudspeaker enclosure structure 10.
As stated above, the two opposite side walls 111 of the hollow housing 11 of the conventional loudspeaker enclosure structure 10 extend linearly backward in a converging manner from the periphery of the opening 110 to the rear wall 112, and this configuration is intended mainly to enhance low-frequency resonance of the loudspeaker enclosure structure 10. More particularly, when transient vibration of the membrane of the low-frequency loudspeaker 120 generates a backward pushing force to the air in the hollow housing 11 (i.e., when the membrane of the low-frequency loudspeaker 120 is displaced backward), the air in the hollow housing 11 flows backward along the backwardly extending and linearly converging side walls 111, making the loudspeaker enclosure resonate at a low frequency. However, once the air flowing backward along the backwardly extending and linearly converging side walls 111 hits the rear wall 112, the air in the hollow housing 11 will bounce back toward the opening 110 due to the compressibility of air. Consequently, vibration of the membrane of the low-frequency loudspeaker 120 is adversely affected. To solve this problem, the cover 12 is formed with the bass reflex port 122, through which the rebounding air is allowed to exit.
Referring back to FIG. 1, while the bass reflex port 122 on the cover 12 can effectively prevent the rebounding air in the hollow housing 11 from compromising vibration of the membrane of the low-frequency loudspeaker 120, the fact that the rebounding air in the hollow housing 11 can exit only by way of the opening 110 on the front side of the hollow housing 11 has its drawbacks. More specifically, some of the rebounding air will cause unnecessary vibration of the cover 12 while the remainder of the rebounding air exits through the bass reflex port 122. Such unnecessary vibration is detrimental to vibration of the membrane of the low-frequency loudspeaker 120 and will result in distortion of the bass notes. Moreover, as all the sound waves in the conventional loudspeaker enclosure structure 10 propagate outward through the opening 110 on the front side of the hollow housing 11, the reflected waves and those which propagate directly out of the opening 110 without being reflected will interfere with each other, causing beats and hence frequency cancellation, if not severe degradation of output sound quality, thus hindering further improvement on the sound quality of the loudspeaker enclosure structure 10. In addition, now that all the sound waves exit through the opening 110 on the front side of the hollow housing 11, the spatial range of sound propagation is substantially limited. In other words, the conventional loudspeaker enclosure structure 10 is incapable of generating a wide acoustic field.
It can be known from the above that the conventional loudspeaker enclosure structures are still flawed in design and fail to provide satisfactory sound effects. Therefore, the issue to be addressed by the present invention is to design a loudspeaker enclosure structure which not only can prevent the air rebounding in its hollow housing from impacting vibration of the membrane of a low-frequency loudspeaker, but also can prevent sound wave cancellation which may otherwise occur if all the sound waves propagate outward through the same opening on the front side of the hollow housing and which, if occurring, will impair sound quality. It is also desirable that the loudspeaker enclosure structure enables multidirectional transmission of sound and hence a wider range of sound propagation than the prior art (i.e., allowing the sound to reach where it cannot if exiting only through the opening on the front side of the hollow housing). In a nutshell, the loudspeaker enclosure structure is expected to precisely provide the desired frequency range or acoustic field.